1. Field of the Invention
The present invention relates to a leadframe, and more particularly to a leadframe used for fabrication of an IC package or LSI package and formed in such a way that the interconnection patterns of a die pad and leads are stamped on a strip of metal sheeting and after the die pads and leads have undergone fabrication processes such as chip-mounting, bonding and packaging, the metal strip is cut into pieces to produce devices.
2. Description of the Prior Art
In recent years, as ICs and LSIs call for increasingly higher level of accuracy and integration, such a lead frame is becoming smaller and thinner with more leads contained therein. In order to avoid the irregularity and deformation of leads during the processes of partial plating, die-pad depressing and bonding, it is necessary to securely retain the leads which are arranged in rows around a die pad, radially extending therefrom.
For securely retaining the leads in place, a polyimide resin film was previously used and the reverse side of such a film was coated with an adhesive made from an epoxy resin. The polyimide resin film is stamped out in the pattern corresponding to the leads of a leadframe and affixed to the leads so as to extend like a strip over their surfaces, whereby the leads can be securely kept together in place.
When a resin encapsulated package is molded, a molding die is set so as to hold the leadframe from its opposite sides, with leads pinched between the upper and lower dies. This often causes clearances between the leads in the molding die and resin is likely to escape from these clearances.
In order to prevent the escape of resin, the prior leadframe is provided with dam bars for connecting the leads of a leadframe which are formed during the pattern formation of the die pad and leads.
Another problem is that high level of integration in ICs and LSIs leads to increased heat generation. It is therefore necessary to take a heat dissipation measure.
In order to dispose of unwanted heat, a heat sink is attached to the outer face of a resin encapsulated package. The heat sink is securely held, being bonded to the leads of a leadframe through a polyimide resin film when a resin encapsulated package is molded. The polyimide resin film is stamped out in a specified pattern suitable for attaching the heat sink and coated with an adhesive made from an epoxy resin at its front and reverse sides.